137 research outputs found
Incised-valley morphologies and sedimentary-fills within the inner shelf of the northern Bay of Biscay
This study is a first synthesis focused on incised-valleys located within the
inner shelf of the Bay of Biscay. It is based on previously published results
obtained during recent seismic surveys and coring campaigns. The morphology of
the valleys appears to be strongly controlled by tectonics and lithology. The
Pleistocene sedimentary cover of the shelf is very thin and discontinuous with
a maximum thickness ranging between 30 and 40 m in incised-valley fills. Thus
the incised bedrock morphology plays a key-role by controlling hydrodynamics
and related sediment transport and deposition that explains some variations of
those incised-valley fills with respect to the previously published general
models
Investigations on the Establishment of Uniform Flow in Compound Channel Flumes
Source: ICHE Conference Archive - https://mdi-de.baw.de/icheArchiv
de Haas-van Alphen oscillations in the underdoped cuprate YBaCuO
The de Haas-van Alphen effect was observed in the underdoped cuprate
YBaCuO via a torque technique in pulsed magnetic fields up to
59 T. Above an irreversibility field of 30 T, the magnetization exhibits
clear quantum oscillations with a single frequency of 540 T and a cyclotron
mass of 1.76 times the free electron mass, in excellent agreement with
previously observed Shubnikov-de Haas oscillations. The oscillations obey the
standard Lifshitz-Kosevich formula of Fermi-liquid theory. This thermodynamic
observation of quantum oscillations confirms the existence of a well-defined,
close and coherent, Fermi surface in the pseudogap phase of cuprates.Comment: published versio
Nernst and Seebeck Coefficients of the Cuprate SuperconductorYBaCuO: A Study of Fermi Surface Reconstruction
The Seebeck and Nernst coefficients and of the cuprate
superconductor YBaCuO (YBCO) were measured in a single crystal with
doping in magnetic fields up to H = 28 T. Down to T=9 K,
becomes independent of field by T, showing that superconducting
fluctuations have become negligible. In this field-induced normal state,
and are both large and negative in the limit, with the
magnitude and sign of consistent with the small electron-like Fermi
surface pocket detected previously by quantum oscillations and the Hall effect.
The change of sign in at K is remarkably similar to that
observed in LaBaCuO, LaNdSrCuO and
LaEuSrCuO, where it is clearly associated with the onset
of stripe order. We propose that a similar density-wave mechanism causes the
Fermi surface reconstruction in YBCO.Comment: Final version accepted for publication in Phys. Rev. Lett. New title,
shorter abstract, minor revision of text and added reference
Lifshitz critical point in the cuprate superconductor YBa2Cu3Oy from high-field Hall effect measurements
The Hall coefficient R_H of the cuprate superconductor YBa2Cu3Oy was measured
in magnetic fields up to 60 T for a hole concentration p from 0.078 to 0.152,
in the underdoped regime. In fields large enough to suppress superconductivity,
R_H(T) is seen to go from positive at high temperature to negative at low
temperature, for p > 0.08. This change of sign is attributed to the emergence
of an electron pocket in the Fermi surface at low temperature. At p < 0.08, the
normal-state R_H(T) remains positive at all temperatures, increasing
monotonically as T \to 0. We attribute the change of behaviour across p = 0.08
to a Lifshitz transition, namely a change in Fermi-surface topology occurring
at a critical concentration p_L = 0.08, where the electron pocket vanishes. The
loss of the high-mobility electron pocket across p_L coincides with a ten-fold
drop in the conductivity at low temperature, revealed in measurements of the
electrical resistivity at high fields, showing that the so-called
metal-insulator crossover of cuprates is in fact driven by a Lifshitz
transition. It also coincides with a jump in the in-plane anisotropy of ,
showing that without its electron pocket the Fermi surface must have strong
two-fold in-plane anisotropy. These findings are consistent with a
Fermi-surface reconstruction caused by a unidirectional spin-density wave or
stripe order.Comment: 16 pages, 13 figures, see associated Viewpoint: M. Vojta, Physics 4,
12 (2011
Rate of Formation of Industrial Lubricant Additive Precursors from Maleic Anhydride and Polyisobutylene
[Image: see text] The Alder-ene reaction of neat polyisobutylene (PIB) and maleic anhydride (MAA) to produce the industrially important lubricant additive precursor polyisobutylene succinic anhydride (PIBSA) is studied at 150â180 °C. Under anaerobic conditions with [PIB] ⌠1.24 M (550 g mol(â1) grade, >80% exo alkene) and [MAA] ⌠1.75 M, conversion of exo-PIB and MAA follows second-order near-equal rate laws with k(obs) up to 5 Ă 10(â5) M(â1) s(â1) for both components. The exo-alkene-derived primary product PIBSA-I is formed at an equivalent rate. The less reactive olefinic protons of exo-PIB also react with MAA to form isomeric PIBSA-II (k(obs) up to 6 Ă 10(â5) M(â1) s(â1)). Some exo-PIB is converted to endo-PIB (containing trisubstituted alkene) in a first-order process (k(obs) ⌠1 Ă 10(â5) s(â1)), while PIBSA-I is difunctionalized by MAA to bis-PIBSAs very slowly. The MAA- and PIB-derived activation parameter ÎG(âĄ)(150 °C) 34.3 ± 0.3 kcal mol(â1) supports a concerted process, with that of PIBSA-I suggesting a late (product-like) transition state
Transport and Phototransport in ITO Nanocrystals with Short to Long-Wave Infrared Absorption
Nanocrystals are often described as an interesting strategy for the design of
low-cost optoelectronic devices especially in the infrared range. However the
driving materials reaching infrared absorption are generally heavy
metalcontaining (Pb and Hg) with a high toxicity. An alternative strategy to
achieve infrared transition is the use of doped semiconductors presenting
intraband or plasmonic transition in the short, mid and long-wave infrared.
This strategy may offer more flexibility regarding the range of possible
candidate materials. In particular, significant progresses have been achieved
for the synthesis of doped oxides and for the control of their doping
magnitude. Among them, tin doped indium oxide (ITO) is the one providing the
broadest spectral tunability. Here we test the potential of such ITO
nanoparticles for photoconduction in the infrared. We demonstrate that In2O3
nanoparticles presents an intraband absorption in the mid infrared range which
is transformed into a plasmonic feature as doping is introduced. We have
determined the cross section associated with the plasmonic transition to be in
the 1-3x10-13 cm2 range. We have observed that the nanocrystals can be made
conductive and photoconductive due to a ligand exchange using a short
carboxylic acid, leading to a dark conduction with n-type character. We bring
further evidence that the observed photoresponse in the infrared is the result
of a bolometric effect
Enhancement and Inhibition of Spontaneous Photon Emission by Resonant Silicon Nanoantennas
Substituting noble metals for high-index dielectrics has recently been proposed as an alternative strategy in nanophotonics to design broadband optical resonators and circumvent the Ohmic losses of plasmonic materials. In this paper, we demonstrate that subwavelength silicon nanoantennas can manipulate the photon emission dynamics of fluorescent molecules. In practice, we show that dielectric nanoantennas can both increase and decrease the local density of optical states at room temperature, a process that is inaccessible with noble metals at the nanoscale. Using scanning probe microscopy, we analyze quantitatively, in three dimensions, the near-field interaction between a 100-nm fluorescent nanosphere and silicon nanoantennas with diameters ranging between 170 and 250 nm. Associated with numerical simulations, these measurements indicate increased or decreased total spontaneous decay rates by up to 15% and a gain in the collection efficiency of emitted photons by up to 85%. Our study demonstrates the potential of silicon-based nanoantennas for the low-loss manipulation of solid-state emitters at the nanoscale and at room temperature
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